The present invention relates generally to telephones and specifically to an apparatus for detecting and annunciating the presence of a dial tone.
Telephones featuring their dialing apparatus located on the handset have recently become commonplace. Operation of such an apparatus requires the user to first bring the headset into viewing position to operate an on/off switch, second bring the handset to the ear for auditory detection of a dial tone, and third remove the handset to a distance at which the dialing controls can be viewed and manipulated. This sequence becomes particularly inconvenient in cases where the user repeatedly terminates a first phone call with the handset controls, and returns the handset to the ear for dial tone detection before returning the handset to viewing distance for dialing the next call.
Another source of delay related to ensuring the presence of a dial tone occurs in telephones having an "automatic redial" feature. An automatic redial feature is circuitry that remembers the last number dialed and redials it at the push of one button saving the user from having to redial all the digits of the telephone number.
This feature frequently incorporates a time delay after an on-hook/off-hook sequence to accommodate the requirement that dialing begin only after a dial tone has been established. This time delay often results in waiting longer than is necessary to ensure the presence of a dial tone and in some instances still might not prevent dialing prior to the presence of a dial tone.